As a method for imparting water repellency to the surface of an article (such as a cloth or fabric product), a method may, for example, be mentioned which comprises dipping the article in a water repellent composition made of an emulsion prepared by dispersing a fluorinated copolymer having units derived from a monomer having a fluoroalkyl group (hereinafter referred to as a “Rf group”) in an aqueous medium, followed by drying the article.
In recent years, EPA (US Environmental Protection Agency) has pointed out that a compound having a perfluoroalkyl group (hereinafter referred to as a “RF group”) with 7 or more carbon atoms is likely to be decomposed in the environment or in vivo to accumulate decomposed products and thus tends to present high environmental burden. Therefore, a water repellent composition has been demanded which uses a fluorinated copolymer having units derived from a monomer having a RF group with at most 6 carbon atoms and having no units derived from a RF group with 7 or more carbon atoms.
As such a fluorinated copolymer, the following fluorinated copolymer has been known.
A fluorinated copolymer comprising units derived from F(CF2)6CH2CH2OC(O)C(CH3)═CH2 (hereinafter referred to as “C6FMA”), units derived from F(CF2)4CH2CH2OC(O)C(CH3)═CH2, units derived from a (meth)acrylate having a C12-22 alkyl group, at least one of units derived from vinyl chloride and units derived from vinylidene chloride, and units derived from a monomer having a cross-linkable functional group (Patent Document 1).